Glass grinding apparatus



July 27, 1937. RB. WALDRON GLASS GRINDING APPARATUS Filed Feb. 8,. 1935 Patented July 27, 1937 UNITED STATES PATENT OFFICE GLASS GRINDING APPARATUS Frederic Barnes Waldron, Prescot, England, as-

signor to Pilkington Brothers Limited,v Liver- 4 Claims.

This invention relates to grinding tools for grinding a travelling strip of glass, and has for its object a grinding tool in which the operative surface is so disposed as to produce a flatter sur- 5 face on the glass and to grind more efficiently.

The operative surface of grinding tools, used in a continuous grinding machine on a travelling strip of glass, and supplied with abrasive at the centre of the tools, is commonly composed of the surfaces of blocks, formed by two sets of grooves, one set leading the abrasive outwardly from the centre, while the other set is circular, and concentric with the axis of the tool.

The outwardly leading grooves serve to enable abrasive supplied at the centre to reach the outer parts of the tool, and the circular grooves serve for the renewal of the spent abrasive. When a quantity of abrasive reaches the operative surface of a block, it travels to the outer edge of this so block while performing grinding work. After doing a certain amount of grinding, it loses its emciency as an abrasive.- Its path from the inner to the outer edge of the block, that is to say, from one circular groove to the next, is such that, bea fore the abrasive becomes spent, it reaches a circular groove and there'becomes mixed with fresh abrasive, so that fresh abrasive reaches the operative surface of the next block outwards.

In the following specifications, grooves servbe termed spreading grooves, and grooves serving mainly to provide fresh abrasive will be termed mixing grooves. Thus in the ordinary form of grinding tool, the spreading grooves are radial and the mixing grooves circular.

Now the glass produced by grinding tools of the above described customary form, is sufficiently flat for many commercial purposes, but certain irregularities in flatness are produced which render the glass unsuitable for certain purposes.

If the annular grinding surface be regarded as divided up into narrow concentric rings, it has been found that irregularities in flatness are produced when the area ofgrinding surface in any one ring differs largely from that in the adjacent rings. Now the condition that the area of grinding surface in any one ring should not differ largely from that in the adjacent rings can be 50 fulfilled by making the mixing grooves elliptical or eccentric, with suitable eccentricity. A grinding tool with such grooves, however, is found to grind unevenly for the reason that the abrasive becomes unevenly distributed round the elliptic or eccentric grooves, being driven by centrifugal ing mainly to lead the abrasive outwardly will force to the portions of the grooves at greater radii.

According to the invention, a disc grinding tool for operating on travelling fiat glass has its operative surface broken up into blocks by two sets of grooves, each block of the majority of blocks having two faces inclined at different anglealess than ninety degrees, to the radius of the tool, so that the outer end of each such face is not behind (with reference to the direction of rotation). its inner end. In a tool for operating on the under surface of the glass, each such face is preferably inclined to the operative surface, so that its edge away from the operative surface is in advance of its edge on the operative surface.

In the accompanying drawing:-

Figures 1 and 2 are each plan views of the operative surface of one-quarter of a grinding tool, showing alternative forms of the invention on a single disc, and

Figure 3 is a plan view of one of the blocks of Figure '2, showing an alternative form of block.

The disc I, with central hole 2, through which abrasive is supplied, has fixed to it, or formed on it, blocks 3. The disc turns in the direction shown by the arrow. In all the figures the blocks 3 are formed by two sets of grooves 4 and 5. The spreading grooves 4 are inclined to the radius, so that their outer portions are in advance of the inner portions. The mixing grooves 5 are at a substantially greater inclination in the same direction. The grooves terminate before the outer edge of the disc, leaving a solid rim 6.

In Figure l, the two sets of grooves are curved, so that their inclinations to the radius increase as the radius increases. In Figure 2, thetwo sets are straight, but the mixing grooves 5 have portions staggered with reference to preceding and succeeding portions, and increase their inclinations in steps.

In the several forms of the tool, the blocks formed by the two sets of grooves (excepting the innermost blocks and the outer rim) have two leading faces inclined to the radius, so that the outer end of each such face is in advance of the inner end.

When the blocks are so formed, by two sets of grooves, the abrasive is evenly distributed, and the blocks can be formed in a variety of ways, of which the three figures show examples, so that the abrasive nowhere has an unduly long operative path before becoming mixed with fresh abrasive and so that no concentric ring of the tool differs largely in grinding area from the adjacent rings. Thus, in the arrangement of Figure 1, taking concentric rings each the width of the grooves 5, the grinding areas, expressed as percentages of the whole area of the ring, in the successive rings, starting from the innermost, are:-

In the arrangement of Figure 2, the corresponding figures are:-

Since, in the customary form of tool with concentric mixing grooves, there are usually three rings having no grinding area at all, each between rings having 60% to 70% of grinding area, the advantage of the arrangements according to the invention is clear.

The invention includes the case where the inclination to the radius of the faces produced by the spreading grooves is zero, but this inclination is preferably a substantial angle.

In the case of toolsoperating on the under surface of a. strip of glass, the invention of our Patent No. 1,956,781, there applied to the single leading face of each block, can, with great advantage, be applied to both the leading faces of the blocks according to this invention. In Figure 3 the block in Figure 2 marked 3' is shown separately, its two leading faces I and 8 being inclined to the operative surface so that the edges of the faces away from the operative surface are in advance of the edges on the operative surface. Thereby the abrasive is forced upwards to the operative surface.

Having described my invention, I declare that what I claim and desire to secure by Letters Patent is:-

1. Disc grinding tool for operating on travelling flat glass, having a solid outer rim and two sets of intersecting grooves, substantially equal in number, the two sets being inclined respectively at different angles, between 0 and ninety degrees to the radius, so that the outer end of each groove is in advance (with reference to the direction of rotation) of its inner end, and a plurality of four-sided blocks of which the sides are formed by the said two sets of grooves, two of the sides thereof facing their direction of travel at such angles that the outer end of each is in advance of the inner.

2. Disc grinding tool for operating on travelling fiat glass, having a solid outer rim and two sets of intersecting grooves, substantially equal in number, the two sets being inclined respectively at different angles, between 0 and ninety degrees to the radius, so that the outer end of each groove is in advance (with reference to the direction of rotation) of its inner end, and a plurality of four-sided blocks of which the sides are formed by the said two sets of grooves, two

.of the sides thereof facing their direction of travel at such angles that the outer end of each is in advance of the inner, at least one of the two sets of grooves having rectilinear portions, the inclination of which to the radius increases with increasing radius.

3. Disc grinding tool for operating on travelling fiat glass, having a solid outer rim and two sets of intersecting grooves, substantially equal in number, the two sets being inclined respectively at different angles between 0 and ninety degrees to the radius, so that the outer end of each groove is in advance (with reference to the direction of rotation) of its inner end, and a plurality of four-sided blocks of which the sides are formed by the said two sets of grooves, two of the sides thereof facing their direction of travel at such angles that the outer end of each is in advance of the inner, at least one of the two facing sides of each block being curved so that the inclination to the radius of any one block is greater than that of a block located nearer to the centre of the disc.

4. Disc grinding tool for operating on travelling fiat glass, having a solid outer rim and two sets of intersecting grooves, substantially equal in number the two sets being inclined respectively at different angles between 0 and ninety degrees to the radius, so that the outer end of each groove is in advance (with reference to the direction of rotation) of its inner end, and a plurality of four-sided blocks of which the sides are formed by the said two sets of grooves, two of the sides thereof facing their direction of travel at such angles that the outer end of each is in advance of the inner, the trailing wall of each of the grooves of at least one of the two sets being so inclined to the operative surface that the edge of the wall away from the surface is in advance of the edge on the surface.

FREDERIC BARNES WALDRON. 

